1. Field of the Invention
This invention generally relates to apparatus for forming corrugated cardboard boxes and more particularly to apparatus for adjusting the position of a flap relative to a panel during the folding operation.
2. Description of Related Art
During the manufacture of paper boxes, paper blanks advance along a paper line pathway for diverse folding and gluing operations. The paper blanks may have "score lines" that divide the blank into sections called "panels" and "flaps". During folding operations, the sections are folded about the score lines to produce the sides, top and bottom of a completed box. In one such folding and gluing operation, preglued edge flaps are folded into a partially overlapping relationship over central, adjoining panels of a blank along certain score lines. The flaps and panels of the blank are glued to produce a completed structure in the form of a folded box.
Prior art apparatus for producing such folding boxes includes a conveyor that engages one or more central panels and advances blanks along a paper line pathway seriatim. The paper line pathway may parallel the score lines that lie between the flaps and adjoining panels. These score lines define the sites of ensuing operations during which the flap is folded about axes, called "fold lines", that are coextensive with the preexisting respective score lines.
As the blank advances along the paper line, it passes below one or more backing bars aligned with the preexisting score lines for a single continuous folding operation. In some apparatus a single continuous folding belt system engages the leading edge of the flap and a contiguous area along the surface of the flap. The belt system comprises a relatively wide belt that runs over a series of pulleys mounted in progressively rotated planes, so the plane of the belt turns from a 0.degree., or initial, plane to a 180.degree., or final, plane. As this occurs, the belt folds the flap onto the central panel. Initially the folding belt system coacts with the backing bar to begin the fold. However, the backing bar usually terminates at a point along the paper line intermediate the folding belt section. This allows the folding belt to force the flap against the panel and produces a sharp, oftentimes creased, corner.
Continuous folding belt systems work quite well with thin cardboard or boxes. However, operating problems can result when these folding belt systems are used to fold flaps onto panels of corrugated cardboard blanks. Apparently these problems arise from the construction of the corrugated cardboard itself. As known, corrugated cardboard blanks comprise paper formed into parallel ridges and grooves sandwiched between cardboard faces. Usually the exterior cardboard faces are finished paper, often with surface printing to appear on the outside of the box. As with other blanks, the corrugated paper blanks have a number of score lines that define the sites for various folding operations.
This inherent variation in folding characteristics manifests itself during both manual and automatic folding operations on corrugated cardboard boxes with some conventional folding box folding apparatus. As a blank is folded along a score line parallel to the grooves and ridges, the actual fold line can skew with respect to the score line. When the fold line does skew, the flap does not register with the central panel. This is particularly evident in conventional paper box folding machines using single folding belt systems.
U.S. Pat. No. 5,092,827 issued Mar. 3, 1992 for An Apparatus and Method for Folding Paper Boxes describes an improved paper box folding machine that folds an end flap onto a central panel in three successive operations as the blank travels along a paper line. At a first station the blank moves along the paper line and a first belt system engages the flap. The entrance to this belt system is in the plane of the blank and the exit is at a plane through the fold line, but angularly displaced with respect to the blank. This angular displacement normally is 90.degree.. At a second station an independent belt system driven by the paper line apparatus through a variable speed transmission engages the partially folded flap and advances it relative to the central portion without any further folding motion. Another folding belt system engages the blank and completes the fold about the fold line at a third station.
The use of a variable transmission at the second station accurately establishes the speed of the belt system with respect to paper line speed. However, such stations are usually located at the middle of a paper line that is physically quite long. They also usually include separate structures for two flaps that operate independently. An operator who makes an adjustment on one side of the apparatus usually must then walk around the paper line to adjust the structure on the other side.
The weight and bulk of such apparatus also complicates the maintenance of a parallel relationship within the second station and between the second station and other portions of the apparatus. This is particularly important when apparatus needs to move to accommodate differently sized blanks. It is difficult to design the best support structure for maintaining the parallelism in such apparatus. Moreover, this weight also may subject the apparatus to premature wear.